The present invention relates to a method for making a printed circuit board using the electrophotographic process and more particularly to a novel method for making a printed circuit board which comprises forming by the electrophotographic process a toner image on a photoconductive layer provided on a substrate for circuit boards by an electrodeposition method and a method for making a printed circuit board in which a toner layer is also formed in the fine through-holes prior to a stripper treatment.
Hitherto, printed circuit boards have been generally produced in the following manner. That is, a photosensitive film is laminated on a laminate sheet comprising an insulating substrate clad with a copper foil, and a photographic negative is put on the photosensitive film. The photosensitive film is exposed through the negative and developed. Then, the undesired copper foil other than the circuit pattern is removed by etching treatment and thereafter, the photosensitive film is removed to form a printed circuit on the insulating substrate. According to this method which uses a photosensitive film, since the photosensitive film is generally thick, namely, about 50 .mu.m, the circuit pattern formed by exposure and development is not sharp and furthermore, it is difficult to uniformly laminate the photosensitive film on the surface of the copper foil and especially it is almost impossible to cover the inside of through-holes.
In an attempt to improve the resolution of the photosensitive film, forming a photosensitive resist on a substrate by electrodeposition method has been proposed in Japanese Patent Kokai (Laid-Open) Nos. 62-262855 and 64-4672. The electrodeposition method can form a uniform thin photosensitive layer as compared with the laminating method. However, photoresists for electrodeposition are generally low in sensitivity. Accordingly, in the case of so-called positive type in which the exposed portions are solubilized in the treating solution, as much as several hundred mJ/cm.sup.2 of energy is required for obtaining a sufficient dissolution and thus, the electrodeposition method is not suitable for carrying out the exposure by a laser. Furthermore, it is difficult to expose the inside of the through-holes to light.
On the other hand, as a method for making printed circuit boards other than the photosensitive resist method, utilization of the electrophotographic process is proposed in West German Patent Nos. 1,117,391, 2,526,720 and 3,210,577 and Japanese Patent Kokai (Laid-Open) Nos. 52-2437, 57-48736 and 59-168462. Japanese Patent Kokai (Laid-Open) No. 63-129689 discloses a method for making printed circuit boards using an electrophotographic photoreceptor having a sensitivity to the wavelength of lasers. This direct patterning of circuits using the electrophotographic process requires a small quantity of exposure of 50-1 .mu.J/cm.sup.2 and semiconductor lasers of low cost and low output can be used. However, the photoconductive layer is provided by coating on a conductive substrate a dispersion or solution of a photoconductive compound and a suitable insulating resin in an organic solvent or by transferring the photoconductive layer once coated on an interim substrate to a conductive substrate by application of heat and pressure. Therefore, the photoconductive layer cannot be uniformly provided in the through-holes.